1. Field of the Invention
This invention relates to mechanical mountings for objective lenses, and more particularly to a mounting mechanism for an objective lens with means rendering it possible to selectively effect visual and manual focusing and automatic focusing.
2. Description of the Prior Art
Recently the field of art of photographic optics has developed a technique for automatically focusing an optical lens system, and various types of automatic focusing apparatus have been proposed, part of which are actually put into practical use as incorporated in cameras. The presently available automatic focusing cameras are, however, restricted to use in a certain working range. For close objects to be photographed, there arises a problem that the focusing control mechanism cannot be operated with an acceptable level of accuracy. To attain the condition of best focus throughout the entire focusing range as the objective lens is axially moved as a whole or in part, therefore, it is required to provide a mechanism for selectively enabling the focusing control to be effected either automatically or manually.
The automatic focusing apparatus is formed either with a light sensitive transducer for producing an electrical signal representing the degree of image sharpness, and a signal processor for finding the object distance to which the focusing movement of the objective lens is adjusted, or so that while the objective lens is being moved, constantly varying electrical signals are processed and upon detection of the condition of sharp focus, the objective lens is arrested. Accordingly, the use of an automatic focusing apparatus of whatever type necessitates a battery as the electrical and mechanical energy source. When all energy of the battery has been used up, and when there is no new battery at hand, the autofocusing camera is no longer operable. It is, therefore, of great importance to provide a manual focusing control mechanism which is built into the mechanical mounting for the objective lens together with the automatic focusing control mechanism so that the focusing can be selectively carried out automatically or manually.